The present invention relates to a laser proximity sensor capable of detecting a distance to a target, and a relative velocity between the target and the sensor. More particularly, the present invention relates to a laser proximity sensor using a laser diode as the transmitter and as a receiver element for coherent optical detection of a laser beam reflected from a target. The present invention will be particularly useful for airborne munitions delivery systems, although persons of ordinary skill in this field will recognize many non-military applications, for example vehicle proximity sensors, laser velocity measurement systems, etc.
While the following application will be particularly directed to a laser proximity fuse for an airborne projectile, it is to be understood that the teachings of this invention are as broad as the appended claims.
Ideal proximity sensors (particularly munitions fusing devices) should share the same essential elements. Such sensors should be small in size (preferrably one cubic inch or smaller); have a minimum number of parts thus reducing complexity, lowering cost, and increasing reliability; have the capability of determining relative velocity between the sensor and a target; and have a wide operating system margin further increasing system robustness. Detection sensitivity must also be very high to ensure a rapid and precise indication of when the target reaches a given distance with respect to the sensor. Ideal sensors should also have a detection range from 0 to 10 meters with a very high resolution within that range. The sensor must be capable of mass production techniques.
Many known proximity detectors are extremely complex and unreliable. For example, infrared (IR) systems are passive sensors capable of being decoyed. In addition, such IR systems are only capable of guiding a projectile to the target for impact explosion and do not provide relative velocity measurement.
Television guidance systems are also known but are obviously not capable of being integrated into less than 1 cubic inch volume. In addition, television guidance systems are extremely unreliable and complex.
Pulsed radar systems are also used as proximity fusing devices. Again, such systems are large and less accurate than may be desired. In addition, the radar beam is a wide beam and thus incapable of careful target discrimination.
Pulsed laser proximity sensors are also known which include a transmit optical section and a receive optical section. The size, weight, and reliability of such systems make them inapplicable for mass production techniques and integration into smaller munitions. Furthermore, the detection sensitivity of such optical systems is very low, and subject to high false alarm rates.
Thus, there is a need for a compact, reliable, accurate, proximity sensor capable of mass production. The present invention proposes such a sensor.